Climate Change Pushing Tropical Diseases Toward Arctic

Temperature changes around the globe are pushing human pathogens of all kinds into unexpected new areas, raising many new risks for people.

He'd gone for a swim in the Gulf of Mexico, whose warm waters, it turned out, would soon kill him. The 31-year-old man arrived at Parkland Memorial Hospital in Dallas three days after his dip in the Atlantic. Crushing pain was radiating from his new calf tattoo—an image of hands clasping a cross along with the phrase "Jesus is my life." He had a fever, and dangerously low blood pressure. Black blisters appeared around his ankles. His kidneys and lungs began shutting down. Gangrenous tissue splotched his hips and toes. Within two months, he was dead.

The culprit, a meddlesome bacterium called Vibrio vulnificus, occurs naturally in warm ocean water. It can seep into scrapes or fresh wounds, including those from tattoo needlework. Infections like the one that killed this man in 2016 have appeared sporadically for years in warm seas from Texas to Maryland. But as greenhouse gases boost temperatures across the globe, rare pathogens like these from hotter parts of the planet are now creeping toward the poles, creating new risks for people. Deadly warm-water Vibrio illnesses are on the rise, now appearing even near the Arctic Circle.

"We are seeing lots of new hospitable areas opening up for these bacteria," says Craig Baker-Austin, a Vibrio expert at the United Kingdom's Centre for Environment, Fisheries and Aquaculture Sciences laboratory in southern England. "Climate change is essentially driving this process, especially warming."

It's no secret that climate change can spread illnesses such as West Nile virus, Zika, and malaria, as rising temperatures push disease-carrying mosquitoes into new places, from the highlands of Ethiopia to the United States. But warm temperatures and shifting weather patterns work in subtle ways, too. Changes in precipitation, wind, or heat are shifting the threat posed by other human illnesses, from cholera to a rare freshwater brain-eating amoeba to rodent-driven infections like hantavirus. And the importance of all these changes are only growing more significant.

"Probably almost everybody is going to feel this at some point in their life," says Stanley Maloy, a microbiologist and dean of the College of Sciences at San Diego State University. "It may be transmission of a mosquito-borne disease in a place it didn't used to be. It may be a simple case of salmonella. But it's going to affect us all."

A Rising Tide of Sickness?

While much attention has been paid to the direct physical threats from climate change, such as rising seas and searing drought, scientists are really only beginning to understand many of the potential disease implications. In part that's because as complex ecosystems shift in complex ways, the behavior response of the smallest cogs in those systems, such as insects and microbes, will be the hardest to predict.

Evidence suggests, for example, that moisture changes could alter the spread of the soil-borne fungi that give rise to the American Southwest's flu-like valley fever, but scientists can't yet say for sure. Infections that aerosolize, like tuberculosis, can linger longer and perhaps be transported easier in regions of the world projected to become more humid. New research suggests the spread of blood-sucking kissing bugs that contain parasites that carry Chagas Disease may well help that affliction spread into North America. Already millions of people worldwide, mostly in South America, suffer from chronic Chagas, which can lead to life-threatening heart damage and stroke.

But there also are plenty of pathogens whose courses already are being altered by fossil fuel emissions.

"So often so many of the things we talk about with climate change are 'this is going to be a problem in 2030 or 2050 or 2100,' and it sounds so far away," says Maloy. "But we're talking about things where our one-degree centigrade change in temperature is already enough to affect infections."

Already in Europe, for example, the ticks that carry Lyme disease, once largely limited to the south, are finding new hosts as far north as Sweden. Some winters aren't cold enough to kill the young nymphs, which also allows them to stick around another season. A similar issue has struck a region near Russia's Ural Mountains, which has seen a 23-fold increase in tick-borne encephalitis in 20 years. Temperature changes have lengthened the tick season by half (the same problem is hammering moose). Meanwhile, the sandflies that host parasites that cause leishmaniasis, some varieties of which cause skin lesions or spleen and liver damage, are showing up in north Texas.

"We have clear evidence in many cases things are happening already, and they're tightly correlated to changes in ambient temperature, extreme weather, or water temperature," Maloy says.

Among the most well-documented of these new threats is the spread of ocean-traveling Vibrio bacteria that can sicken or kill unsuspecting swimmers or shellfish eaters, even though these bacteria need warm water to survive.

Link to Rising Temperatures

There are more than 80 species of Vibrio, at least a dozen of which are pathenogenic to fish and humans, including the bacteria that causes cholera, which afflicts millions of people around the world and kills 100,000 a year. Non-cholera species sicken more than 50,000 Americans a year, mostly with mild nausea, mostly from eating tainted shellfish. But a small subset are hit with deep infections, like the man in Dallas, as bacteria enters the bloodstream through fresh wounds.

In his case, the impact was extreme in part because he'd been a heavy drinker—regularly downing six beers a day—and people with liver diseases are even more susceptible.

"He became very sick very quickly," says the physician who treated him, Nicholas Hendren, an internal medicine resident at Parkland Health and Hospital System and the University of Texas Southwestern Medical Center. He published a case report in a British medical journal. Hendren compared the runaway nature of the infection to "a truck going down the side of a mountain without any brakes."

The pain can be immense, according to Wendy Billiot, a former Louisiana fishing guide who caught a Vibrio infection in just one middle finger in 2012. She'd been guiding a group in the Gulf of Mexico, and spent the day cracking crab to bait their fishing hooks, never noticing that the rough shell of the crab had scraped her middle finger raw, providing a pathway for the bacteria. Four days later her finger was turning purple and, not knowing what was wrong, she went to the doctor's office.

"I've got a high pain threshhold, but I've never felt anything so excruciating in my life—and I've had six children," she recalls. "I was very fortunate I didn't lose my finger, my hand, my arm, my life."

The risks to humans can be significant. The bacteria grow quickly when temperatures reach 13 to 15 degrees Celsius, which long has been normal in summer in the gulf and in some Atlantic estuaries like those near Chesapeake Bay. But lately cholera cases have been multiplying around the globe. Increasing, too, are non-cholera Vibrio sicknesses. The one constant variable—rising temperatures.

Before 2004, for example, Alaskan waters were thought to be too cold to support enough Vibrio to cause disease. But around July 4 that year, aboard a small cruise ship, several dozen passengers got sick after eating oysters from the Gulf of Alaska—more than 1,000 kilometers further north than the previous northernmost Vibrio incident. The waters that summer around the oyster beds were 2 degrees warmer than they'd ever been.

"What's happening here is related to climate change—no question," says Jay Grimes, a microbial ecologist at the University of Southern Mississippi's Gulf Coast Research Laboratory.

Then a recent study of 60 years of marine plankton surveys all along the North Atlantic and North Sea found that a dramatic rise in Vibrio populations tracked with increasing sea surface temperature—and with unprecedented Vibrio infections along the coast in Europe and the United States eastern seaboard.

Nowhere had those outbreaks been more dramatic than in the Baltic Sea in 2014, when a rash of Vibrio-related illness finally hit where they were least expected—northern Scandinavia. A cluster of people from high counties along the coasts of Finland and Sweden were struck by a host of these pathogens. Victims ranged from age 3 to 93. They faced debilitating sores and skin lesions. Some suffered dangerous blood poisoning. A few nearly lost organs and limbs. One died.

Ultimately, 89 people were sickened—all after bathing in an unusually balmy Baltic. The incidents marked the largest number of Vibrio cases ever in each country; six people were infected along the 65th parallel—less than 200 miles from the Arctic Circle. They were the northernmost Vibrio infections ever recorded. And no wonder: That summer, for the sixth time in 20 years, northern Scandinavia experienced another record-breaking heat wave, with temperatures that topped 20 degrees Celsius for several days. Temperatures hit highs not seen in recorded history.

"I was really surprised to find infections at these latitudes," Baker-Austin says. "This is an environment that is frozen for a good part of the year. Climate warming has greatly expanded the range over which these bacteria can proliferate—with wide ranging impacts on associated infections."